Radio communication system



Jan. 8, 1946. DE wlTT R. GODDARD 2,392,585

RADIO COMMUNICATION SYS-TEM Filed Nov. '11, l1945 5 Sheets-Sheet l .EN .hwg

E E Q m0 ED, N W05@ T R 1/ W Dv\Q\ M I W N\ lll momma@ Y #SEG Jan- 8, 1946- DE wlT'r R. cuaommm'n 2,392,586YM RADIO COMMUNICATION SYSTEM Filed Nov. 11 1945 s sheets-sheet 2 #5K/mw A TTORNEY Jan. 8,1946. DEwn-r R. GODDARD 2,392,585`f Y RADI' COMMUNICATION SYSTEM Filed Nov. 11, 1945 s sheets-sheet' 3l A TTORNEY Patented Jan. 8, 1946 RADIO COMMUNICATION SYSTEM De Witt R. Goddard, Riverhead, N. Y., assignor to `Radio Corporation of America, a corporation of Delaware Application `N ovember 11, 1943, Serial No. 509,872

17 Claims.

This invention pertains to signalling systems and particularly to improved short wave radio communication systems.

The signal emitted by an 'amplitude modulated transmitter varies in power `from moment to moment depending upon the depth of modulation. Therefore, a receiving set using an automatic Volume control must have its timeconstant adjusted to a value such that the automatic contol will not respond to the lowest audio frequency that it is desired to receive or some of the modulation will be suppressed, giving` rise to distortion. As a consequence, high intensity static crashes pass through the system and appear at the loud speaker thereby reducing the intelligibility of the incoming signal and causing great annoyance. These high intensityv static crashes are frequently within the modulation range or above so that .the slow automatic volume control systems known heretofore do not act quick enough to suppress the same.

In my new and improved system as described herein, it is made possible touse an extremely fast automatic volume control without affecting the modulation. 1n my `system the time constant of the automatic volume control can be and is adjusted to a frequency higher .than the highest modulation frequency `to which the modulation amplier system will respond.

With ordinary fading my automatic volume control will hold the signal steady vin my improved system. Shouldstatic crashes, loud clicks etc., occurring in the house lighting supplyeto., be picked up by thereceiver, their intensity in the audio system can never rise abovea fixed value determined by the setting of the volume control. This value is approximately equal to that of the incoming signalv when modulated 100%. In my system, if a static crash of very high intensity occurs at a moment when the transmitter is being modulated v100% there will be practically no rise in speaker volume` asftlie automatic volume control yallows only a deiinite voltage to be detected, be it signal statioor a combinationof both. 'As a consequence, in my system all loud sharp y"crashes, that are so annoying, are suppressed in the loud speaker. Intelligibility is increased since it is well known that a sudden loud noise of short duration reduces the sensitivity of the ear for "a comparatively long time.

In describing my invention in "detail reference willbe made to the attached drawings wherein Fig. l is used to illustrate the operation of my system.

Fig. la illustrates therelation of the carrier and its side bands radiated by a system modulated in accordance with my invention.

Fig. 2 illustrates mainly by block diagram and schematically a modulation system arrangement in accordance with myinvention.

Fig.. 2a illustrates a modification of the arrangement of Fig. 2.

Figs. 3, 4 and 5 illustrate by rectangles and schematically three forms of receiving systems adapted to the reception .of energy transmitted by the system as illustrated .in Fig. 2. 'The receivers have fast automatic volume controls which suppress static without affecting the modulation. s 1 n y The desirable effects described above, and other valuable features to `be described later, are obtained in the following manner. In accordance with rmy invention a transmitter is modulated nearly by a l0 kilocycle tone, which is in turn modulated nearly 100% by the signal. The transmitter is also modulated by the signal. In this modulation process the signal modulation of the transmitter carrier and the modulation envelope of the tone are caused to be out of phase, that is, are opposed. This provides an output as illustrated graphically in Fig. la. The essential featurel is that the modulation it is desired to transmit is impressed both on ,the 10 kilocycle tone and on the carrier but in such a way as to modulate the 10 kilocycle,v tone and the carrier in substantially exactly .reverse phase relation. Therefore, in ordinary broadcast modulation frequencies the depth of modulation on the transmitter remains essentially `constant, because when the power in B and B l increases the power in A decreases and vice versa.

This will be clearer if one considers rst two independent RF carriers separated say 15 kilocycles, and indicated in Fig. 1 by carriers X and Y. One of them, say X, is amplitude modulated in the conventional fashion, while Y is,

modulated the same amount with the modulation in opposed phase relation.

Now, it is evident that the power is constant in a receiver having a band width suicient to include both carriers and their associated side bands. Therefore, an extremely rapid AGC (automatic gain control) Vsystem may be applied to this receiver without in any way affecting the modulation of either carrier. If, after the application of this automatic gain control, ,carrier X and its associated side bands be ltered off of the signal, it, may be demodulated in the conventional manner yielding the original 2 Y modulation. The carrier Y will likewise yield the signal.

It is evident that by virtue of the rapid automatic gain control, rapid with respect to the modulation frequencies, staticcrashes will affect the gain of the receiver. The gain of the receiver will drop with sufficient rapidity to prevent powerful static crashes from appearing in the AF outputwith greater amplitude than the maximum modulationcomponents.

Fig. 1a illustrates the relation of the side bands radiated by a transmitter modulated in accordance with my invention. In the illustration it is assumed that the modulated tone is of kilocycles, but it will be understood that other tone frequencies may be used. In Fig. 1 A represents the carrier, while B and Bl 'represent the two side bands caused by modulation of the carrier by the signal modulated 10 kilocycle tone. a, a are the Y side bands of the carrier A'and are caused by modulation of the carrier. b, b and b', b are the side bands of B and BI caused by modulation of the tone frequency.

Fig. 2 shows in a simplified manner Va transmitter arrangement in accordance with my invention, and modulated as described above to fulfill the requirements of Ya system in accordancel with my invention.y In Fig. 2 the signal that it Y is desired totransmit originates at a studio or other source indicated at D. This audio signal passes into a transformer R which has two sec- .ondaries I2 Yand I4. The secondary |2 is cou- Y pled to an amplitude modulator E to feed theretothe signal for amplitude modulating therein A the oscillations supplied by the source |0,.which,

as stated above, may have an output at 10 kilocycles. The output of the modulator E which is a modulated tone, isrfed to the primary winding I6 of a transformers having kanother primary winding' |8 coupled by winding I4 of transformer R to the source D. The modulation envelope'on the modulated tone supplied to I6 and the modulation itself supplied to I8 are 180 out of phase.

The secondary winding of transformer S feeds a modulation system included in the rec- Jform'er S and a superaudible tone is supplied through amplifier toY theother winding I6 of transformer S. In this modification note that the tone is not modulated directly by the signal `but is modulated indirectly thereby in( an inverse sense, as will appear hereinafter. The tone and the signal modulate the carrier in F, and after the desired amplification in ampliers'also in F i the modulated carried is transmitted. A small ramount of the output is bled off by the lead including resistor 2| and rectified in 23.

The rectied current is fed from the rectifier inV 23 through a time constant network 25 that operates rapidly V.with respect to the modulation frequencies but slowly with respect to the 10 kc. tone carrier. controls the gain of the amplifier? in in a well known manner and the controlis. in. afordane The output of the network in 25` with signals.y This results in modulating the tone in the amplifier in accordance with the signals and in such a sense as to keep the Vradio frequency powerV in the antenna substantially constant. That is, this power is constantras far as the modulation frequencies are concerned. Thus, we againhave in the output of thetransmitter at F currents which are represented graphically as inFig. 1a. Here, as in Fig. 2, the source I0, am-

plifier H, transmitter F, rectifier'23 and time In Fig. 3 the transmitted carrier is pickedl up` on the aerial 29 and fed to a radio frequency amplifier 30, wherein it is amplified and fed to a mixer for heterodyning against oscillations from a source 3|. The intermediate frequency is selected from 30 and Vfed to anV intermediate frequency amplifier 32 which has a band pass sufficiently wide to pass the radiated carrier the side tone frequencies and the modulation side bands on the carrier and side tones. For example, 30 kilocycles are passed by the intermediate frequency amplifier in 32. 32 also includes a mixer tube .wherein the intermediate frequency energy is heterodyned with oscillations from a source in 33 and the resultant energy is impressed on an auwith its modulation side bands.

tomatic volume control system 36 and on three Yfilters 38, 39 and V40 arranged to pass modulation/corresponding to the side bands on the upper side tone BI, the side bands on the carrier A and the side bands on the lower tone B. v

The intermediate frequency out of the 30 kilocycles IF amplifier and mixer in4 32 is fed to the automatic volume control system in 36 wherein itis rectified and used to control the gain ofthe l Aamplifiers or an amplifier in unit 30 and in unit The output Yof the amplifier in 32 is also fed toe: the three band pass amplifiers 38, 39 and 40. In

the system illustrated the band passwidth of the filters in 38, 39 and 40 is 10 kilocycles., Filter 38 passes say the 10 kilocycle side band BI of Fig. 1a, Y Filter 39 passes the main carrier A and its modulation side bands. Filter 40 passes the 10 kilocycle side band B and its modulation side bands. Thethree ampliers 38, 39 and 40 include detectors.- The'output of the detectors in 38 and 40' are connected in parallel and pass to one grid and the cathodes of aV of phase. Note'as described above, side'bands carriersBandV Bland'their `side .bands are in phase with each other, but are opposed to main carrier A and its side bands.

Since, as stated above, the received modulated carrier peaks reachy the same value irrespective of the extent of modulation (the modulation depth varies) the fast automatic volume control 36 etc., may be adjusted to prevent a rise -in the output volume which exceeds that intensity which represents full modulation. suppress the modulation but does suppress static and noise of a frequency higher than the highest modulation frequency. In other words, my control means presents to the detector in the receiver a definite adjustable voltage either signal or noise yor static or a combination of the same. 'Of course the time constant of this automatic volume control should be such that it doesnot suppress potentials of the frequency of the modulated tone used at the transmitter being in the example given 10,000 cycles.

The arrangement of Fig. 4 makes use of frequency diversity. In this arrangement there are present at the output of the intermediate frequency amplier 32 three frequencies 10 kilocycles apart as was seen in the description of Fig. 3. Each of these frequencies are modulated. In addition to the high speed automatic volume control 36 shown and described in Fig. 3, there is added in Fig. 4 additional detector tubes 50, 52 and 54 coupled to the outputs of the filters 38, 3e and 40. These additional detector tubes detect the outputs of the detectors and filters of 38, 39 and 40, and provide selective volume control potential in the resistor 60. That is, the plates of these tubes 5U, 52 and 54 are all fed from a common source 56 through the resistor 60 `and the Voltage drop across the resistor 60 is used byway of lead 62 to supply bias to one or more tubes in the filters, amplifiers and detectors in units-38, 36 and 40. This bias varies the gain of the intermediate frequency amplifiers in thesel lters simultaneously. Therefore, if any one of the three signals is appreciably stronger than the other two signals, it will be used for control purposes, while the other two amplifiers will have their gain re- .duced to suppress the output thereof. This operation per se, it is believed, is well known, having been described and claimed in John B. Moore, U. S. Patent No. 1,849,632, dated March 15, 19,32. This volume control arrangement including tubes .50, 52, 54, source 56 and resistance 60, necessarily has a sufficiently long time constant to prevent modulation frequency distortion.

In a modification illustrated in Fig. 5, a plurality of receivers 65, 61 and 6.9, similar to the one shown in Fig. 3 are used. By spacing the aerials of these receivers space diversity is obtained. Here each 30 kilocycle band pass amplifier 32, 32 and 32" has part of its output passed through a separate automatic volume control detectorV tube in unit 36. The platesvof these detector volume control tubes are connected in a manner similar to the manner in which the plates of the detector tubes 50, 52 and 54 are connected in Fig. 4 to control the gain of the `amplifiers in `32, 32 and .32. 'Ihe arrangement is such that the output of the amplifier wherein the strongest signal is received takes control primarily as describedvin the above identified patent. Howeverythetime constant of the volume control. in this system is made vfast as in Fig. 3, to suppressstatic and othernoises ofthe same character and frequency. The outputs of the 30 kilocycle band pass ampli-fiers andhetero- Thus my means does not.

dynes in 32,132 ,and .32" are ed ltofsecond-intermeidiatefampliers `*'HJ, 1.2and I4, and thence to individual kpushpull .amplifiers 80, .2,82 and 84 and from the sa-id .amplifiers to :zi-combining .-unit in .86 from which-the combined and amplified.modulation is derived. Each of. .the second intermediate frequency .amplifiers TH), 12vand 14 include `three bandpass filters similar to iilters .38, 3.9 and 40 .of Figs. 3 and 4 #which .pass the bands Bl, A and `B. These `filters and second intermediate frequency ampli-tiers .also include detectors. Moreover, the outputs of the several band pass filters .and `detectors in each unit 10, 1,2 and 14 yare combined in pushpull in amplifiers 80, 82 and V8l! in the manner shown and .described vin connection with-Fig. l. That is, each unit 10 has a lterand ldetector for the side band carrier B and its sidebands: lthe carrier A yand its side bands, and the side band carrier vBI and its side bands. Moreover, the 1detested outputs of the detectors for B andBI are combined yin phase and the-combined .outputs combined with the detector for Ainpushpul-l relation. The outputs of the pushpull amplifiers 8.0, 82 `and-Mare combined.

-In Fig. 4 the modulation Voutput yis derived in the sam-e manner .as .in Fig. 3. That is, the outputs of the detectors in the filters passing .current characteristic of B` and Bl and their side bands are added in parallel and this energy and the output `of the detector in the `filter' passing the current'characteristic of the carrier A and .its side frequencies are applied in `pushpullto 7the pushpull amplifier in 46. In Fig. 4, thefrectifiers Sil-provide automatic gain control with diversity effect. In Fig. v5 the -circuits in unit 1|) and unit include three filters and detectorssuchas 38. 39 and 40 of Fig. 3, and a pushpull ampliilerias in 46 of Fig. 3. The same'remarks'applytounits 1,2 and 82,and units -1'4 and. of Fig. 3.

vI claim:

l. The method of signalling with signal currents and .carrier currents, and loscillationsof superaudiblefrequency which includesithese steps, modulating'the oscillations in raccordance with the signal currents, and modulating the carrier currents in accordance with the signal currents and signal modulated oscillations with the signal modulations and` the modulations on the oscillationsY opposed to provide a modulated carrier the total power of which is substantially constant during` operation.

*2. The -method of signalling which includes these steps, Vgenerating loscillations of carrier wave frequency, generating other oscillations of carrier wave frequency, deriving currents characteristie of signals, modulating said rst oscillations in accordance with said currents, modulatingsaid first oscillations in accordance with said other oscillations and modulating said other oscillations,

irl-accordance with said currents and in a sense such that the modulations on the otherV oscillations .oppose the first mentioned modulations on said first' oscillations'.

3. The method of signalling with oscillations of carrier Wave frequencyand oscillations of superaudible frequency which includes these steps, modulating-said oscillations of superaudible frequency inaccordance with said signals, modulating said oscillationsof carrier frequencyby said signals .and by said modulated oscillations of s11- peraudible frequency while maintaining the modulation envelopes in opposed relation onsaid carrier.

.4. The lmethod Vof signalling which includes these steps, kgenerating oscillations of carrier'wave f tions'derived from theside frequencies and corncillations with the signals with themodulationA envelope of the oscillations in opposed relation with respect to the signals during the combination'and modulating carrier Wave energy in accordance with the combined energy to derive modulation energycomprising the carrier and upper and lower side bands corresponding to the generated oscillations with the carrierand the side `bands each having as side frequencies the signal frequencies. 1 Y j Y6. The method of signalling which includes these steps, generating oscillations of carrier wave frequency, generating oscillations of lower frequency, generating signalling currents, modulating said oscillations of carrier wave frequency in accordance withV said oscillations of lower frequency and in accordance with said signalling currents, rectifying the resulting modulated carrierand controlling the amplitude of the oscillations of lower frequency used to modulate said oscillations of carrier wave frequency in accordance with rectified output components of a fre- Y quency below the highest signal current'frequency;Y Y. Y

7. The method of demodulating wave energy modulated as recited in claim 1 which includes these steps, amplifying wave energy characteristic of the said carrier and its two side frequencies with the signal modulations on each thereof, rectifying said energy, deriving from said rectied energy potentials ofthe frequency higher'than the highest signal frequency, controlling the ampliiication of said modulated wave energyY in accordance with said derived potentials, and demodulating said energy the amplification of which is controlled to derive therefrom the signal modulations. Y

8. The method of demodulating wave energy modulated as recited in claim 1 which includes these steps, amplifying wave energy character,-

bining this resulting energy with the signal modulations derivedY fromV the said carrier Vdifferentially. f, I

1 10. The signalling method including these steps, generating oscillations of carrier wavefrequency, generating oscilations of sub-carrier frequency, modulating said iirst carrierY in accordance with signals and in accordance with said sub-carrier oscillations, modulating saidsub-carrier in ac.-V cordance Awith signals, and inasense Vsuch Vthat Y the modulation envelope on the subi-carrier modulations on said first carrier oppose the ,modulation envelope of the signal' on said first carrier, sending the modulation energy to a receiver,`at the receiver, amplifying the received energy, deriVing from the amplified energy potentials which depend upon the amplitude thereof, controlling the amplification of the modulation received enistic of said carrier and its two Y side frequencies with the signal modulations on each thereof, rectfying said energy, deriving from the rectified energy Vpotentials which recur at a rate above the highest signal current frequency and `below the frequency of said' other oscillations,

controlling the amplification of said'modulated Wave energy in Vaccordance with said derived potentials, and demodulating said modulated energy the amplification of which is controlled to' derive therefrom the signal modulations.Y

9. VThe method of demodulating "wave energy modulated as recited in claim 1 which includes these steps, amplifying wave energy characteristie of rthe said carrier and its two side frequencies with the signal modulations on each thereof,

Y rectifying said energy to deriveY a potential to control at a rapid rate the amplification of said energy, demodulating said energy the amplifica- Y tion of which is controlled to derive therefrom the signal modulations on said carrier and its two side frequencies, combining the signal modulaergy in accordance with the derived potentials,

and deriving from the received and amplified en" oscillations, modulating said sub-carrier oscilla-v tions in a sense such as to produce an output comprising as a main carrier said first carrier and as upper and lower' side carriers the sum and difference of said iirst carrier and sub-carrier with modulation on each carrier, sending the modulation energy to a'receiver, at'the receiver amplifying the modulation energy, deriving from the amplified energy potentials which vdepend upon the amplitude thereof, controlling the amplification of the modulation energy in accordance with the derived potentials, and deriving from theamplilied energyzthe signal modulationslV i Y' V 12. The signalling method including these steps,

i generating a sub-carrier, modulating said sub-car- Y thereof, utilizing said Vpotentials to control the` amplification of the modulated energy, deriving from said heterodyning process modulation corresponding to that impressed on the .carrier and on the sub-,carrier considered as side bands of vthe said carrier, combining the modulation cor-V responding to the modulation onkthe [said side bands and dilferentially combining the said comloined energy with the modulation corresponding to the modulation on said carrier.

13. In a signalling system a source of Aoscillations of carrier wave frequency, a source of oscil lations of lesserrfrequency, a source ofesignals,

Y means for modulating oscillations from said source of oscillations of lesser frequency vinaccordance with signals from said source ofsig-Y nals, and means for modulating oscillationsfrom said source of oscillations of carrier wavefrequency in accordance with the signals and the modulated oscillations ofY lesser frequency Vand an output-coupled to said last named means.

14. In a signalling system a source of/oscillations of carrier Wave frequency, a source of oscillations of lesser frequency, a source of signals, means for modulating oscillations from said source of oscillations of carrier wavejrequency in accordance with signals and in accordance with oscillations from said source of lesser frequency, and means for controlling the amplitude of the oscillations of lesser frequency in accordance with the signal modulations on said oscillations of carrier frequency.

15. In a signalling system a Wave energy pickup means, a radio frequency ampliiier and a detectoi and a source of local oscillations coupled thereto, a band pass filter, a detector and a source of local oscillations coupled to said first named detector, an automatic gain control circuit having a small time constant and including a rectier with its input coupled to said second mentioned detector and its output coupled to ampliflers in said first mentioned stages, three lters having their inputs coupled to said second detector, a detector for each filter, a pushpull amplier and connections for impressing the output of two of said last mentioned detectors and the output of the remaining one of said last mentioned detectors in pushpull relation on said pushpull amplifier.

16. A system as recited in claim 15, including a rectifier coupled to each of said three detectors, an impedance in series with all of said rectifiers and connections from said impedance to stages in said filters to control the gain thereof.

17. In a signalling system a plurality of wave energy pickup means, a detector and a source of local oscillations coupled to each of saidpickup means, a band pass filter, a separate wave amplifier, a second detector and a source of local oscillations coupled to each of said first named detectors, an automatic gain control circuit coupled to each of said second detectors, each of said gain control circuits having a small time constant and including a rectiiier with its input coupled to a different one of said second mentioned detectors and its output coupled to said amplifiers, three filters coupled to each oi.' said second detectors, a pushpull amplier for each group of filters and connections for impressing the output of two of said filters of each group and the output of the remaining lter of each group in pushpull relation on a diierent one of said pushpull amplifiers.

DE Wrrr. R. GODDARD. 

